1. Field of the Invention
This invention relates to multiplexing techniques for obtaining status of a plurality of switches disposed at a remote location in the form of a matrix keyboard that connects to a controller by a single wire bus and, more particularly, in a preferred embodiment to systems for generating visual displays at a remote instrument panel indicative of the status of each switch of the matrix, the switches being separately scanned by a switch scanner that connects at a single point to the bus and controlled by a microcomputer within the remote instrument panel.
2. Description of the Prior Art
Scanning matrices of switches or keys of a keypad has generally been performed by microcomputers or controllers using complex software. Where separate keyboards are employed, a serial link between the controller and the keyboard usually improves reliability and saves on cable usage but further complicates the protocol between devices. Also, with matrices of switches, a problem sometimes exists in effectively addressing the switches.
In an effort to place a matrix of switches at a remote location and use a minimum number of wires between the controller and the matrix, a search was initiated for a scheme that would use as few as a single wire between devices as well as to manage control of the scan pulses used to scan the switches. That search resulted in the improved matrix scanner system of the present invention.